The Washington Post has the full story on this, (and this graphic which shows the problems) along with some video of the inside of the monument with tourists racing for the stairs during the earthquake as debris falls down on them. Amazingly, no one was injured. A full assessment of the exterior stones begins this week with man rappelling down the sides of the monument.
The entire interior and exterior was restored in 1999 and, during that process, each stone was numbered, photographed and catalogued so that they will be able to compare their condition before and after the earthquake. It's amazing that the earthquake wrought such havoc on the monument which has been standing there since 1884. But, unlike modern office buildings of the same height, there is no steel frame that can sway and counterbalance with the movement. It's just stones and mortar and, when shaken up, it simply starts to fall apart.